This invention relates to a fabric softening composition and to methods of treating fabrics in order to enhance their water absorbing capabilities.
A fabric softener is a dilute solution or dispersion of a quaternary ammonium derivative used to treat fabrics in the final rinse of a laundering process in order to make the fabrics feel softer. In addition to softness, fabric softeners are known to also provide fluffiness control. Because of the affinity of quaternary ammonium compounds for negatively charged surfaces, their single largest market has been as fabric softeners. Commercial fabric softeners generally include about a four to eight percent dispersion of quaternary ammonium compound which is added to the rinse cycle of the washing process. The quaternary ammonium compound can also be applied to a nonwoven sheet or a polyurethane foam which is added with wet clothes in a dryer. Such sheets contain a fatty acid ester which allows the quaternary ammonium compound to transfer from the sheet to the clothes in the dryer during the drying cycle. Recently, there have been devised combined detergent and softener formulations which allow introduction of all additives in the wash cycle.
Modern washing machines work automatically and the operator places the laundry in the machine, pours in the detergent, and sets the controls. One set of controls determines whether the machine employs hot, warm, or cold water. Water enters the machine through hoses connected to the hot and cold water pipes. The operator also sets controls in order to select the length of washing and rinsing time, and the amount of water that enters the machine. The machine is powered by an electric motor and includes a filter that removes lint, and automatic dispensers for bleach and fabric softeners. A wash cycle typically includes four stages. In the wash cycle, after water fills the wash tub, an agitator reverses direction alternately and moves the laundry through the water and detergent, and forces water through the items of laundry. The washer is then emptied of all of the wash liquor in the spin cycle and the clothes are spun to remove excess water. In the rinse cycle, clean water is added along with the fabric softener and the clothes are again agitated. The washer is emptied of rinse liquor and the clothes are spun in a final spin cycle during which time excess water is removed and pumped out of the machine through a drain hose. The clothing is then ready to be removed from the machine and dried in a dryer or hung on a clothesline until dry.
Fabric softeners for use in such machines are well known in the art. For example, in British Pat. No. 1,549,180, issued July 25, 1979, Dumbrell et al disclose a fabric softener which includes, in addition to the softening benefit, the additional benefits of easier ironing, antistatic properties, pleasanter feel, and soil release properties. The additional benefits are stated to be derived from the inclusion along with a cationic quaternary ammonium fabric softening agent, of a silicone compound which is said to be an aqueous emulsion of a linear siloxane.
The Dumbrell et al Canadian Pat. No. 1,085,563 is a version of the United Kingdom Patent. The Canadian Patent elaborates as to the meaning of the term "predominately linear" of the United Kingdom Patent, and on page 6, in the last paragraph, the Canadian Patent specifies that a "limited degree of cross linking can be tolerated". The materials of the present invention, however, are "highly" branched and crosslinked materials containing at most less than forty percent of linear silicone polymer and hence are quite distinct from the materials employed in either of the related Dumbrell et al United Kingdom and Canadian Patents. In fact, on Page 10, the Canadian Patent specifies that a crosslinked silicone is outside the scope of the invention.
Specifically, Dumbrell et al relate to fabric softening compositions that include an aqueous dispersion of a cationic softening compound, and a silicone emulsion. The cationic compound is disclosed to be one or more or mixtures of a combination of quaternary mon-ammonium compounds such as tallowtrimethylammonium chloride, and ditetradecyldimethylammonium chloride; quaternary imidazolinium compounds; polyammonium compounds such as acid salts of diamine compounds, and polyamine salts; and polyalkyleneimine salts. The silicone emulsion is preferably a linear dialkyl or alkylaryl siloxane which may be partially or wholly fluorinated, or substituted with cationic nitrogen groups. The viscosity is disclosed to be, at twenty-five degrees Centigrade, at least one hundred and up to eight thousand centistokes. The weight ratio of siloxane content of the emulsion to the dispersion is five to one, to one to one-hundred. Representative compositions are said to be cationic emulsion polymerized dimethylsiloxanes, with the emulsifying agent being, for example, ditallowyldimethylammonium chloride; quaternized polysiloxanes such as dipyridinium polydimethylsiloxane; and aminofunctional linear polysiloxanes such as polydimethylsiloxanes containing dimethylaminopropyl groups.
Silicone polymers can be classified as being linear, branched, or crosslinked. This classification is commonly accepted and is used in the silicone industry. Branched or crosslinked silicone polymers are prepared by the incorporation of an alkyl trisiloxy unit into the siloxane polymer chain. Crosslinking results when two alkyl trisiloxy units are connected by a segment of the polymer chain during the polymerization process. The number of polymer branches which react with another polymer (or a different alkyl trisiloxy unit on the same polymer) to form crosslinks is a function of the amount of alkyl trisiloxy units present, and the reaction conditions. It is generally accepted in the industry that the inclusion of alkyl trisoloxy units will lead to branching and crosslinking when polydiorganosiloxane is prepared via addition polymerization. Because of the random nature of this polymerization, however, alkyl trisiloxy groups will not be incorporated into all of the polymer chains; some linear polymers will normally be present in such systems. Incorporation of a methyl trisiloxy unit into a polydimethylsiloxane results in a branched and crosslinked siloxane and not a linear siloxane. The use of the branched and crosslinked fluids in a rinse cycle fabric softener is not taught in Dumbrell et al since the incorporation of a trisiloxy unit into the linear siloxane polymer chain creates a branched and crosslinked siloxane that has significantly different properties. For example, linear siloxanes are soluble in toluene whereas branched and crosslinked siloxanes are not. Thus, a toluene solubility test provides a simple method to distinguish between linear and nonlinear polydimethylsiloxanes. In addition to differences in solubility, linear and nonlinear polydimethylsiloxanes exhibit different physical properties. Linear polydimethylsiloxanes are liquids which exhibit viscous flow, even at high molecular weights. Branched or crosslinked polydimethylsiloxanes of comparable molecular weight are elastomers. The properties of the silicone polymer in an water-based emulsion is conveniently determined by "breaking" the emulsion by adding large amounts of salt or alcohol, or evaporating the water and examining the residue. Since the two classes of siloxane polymers have such significant differences in physical properties, it would not be obvious to substitute a branched and crosslinked siloxane for a linear siloxane in fabric softener applications.
In accordance with the present invention therefore, a branched and crosslinked silicone emulsion is employed in contrast to the linear material of Dumbrell et al. More importantly, it has been found that the use of an emulsion of nonlinear silicone provides certain advantages neither taught nor appreciated by Dumbrell et al. For example, softener treated fabrics in accordance with the present invention possess enhanced rewettability or improved water absorbency, in addition to softness, and this benefit was neither realized nor contemplated by Dumbrell et al. Thus, while Dumbrell et al observed a series of benefits resulting from the incorporation in the softener formulation of a linear silicone material, the rewettability property of the present invention was not one of the benefits discovered by Dumbrell et al, nor the feature of branching or crosslinking in general. In the present invention, therefore, water absorptivity or rewettability of fabrics treated with hydrophobic softening agents is significantly improved, as is softening by the use of branched and crosslinked silicone fluid emulsions. The use of hydrophobic silicones as taught herein to improve water absorbency of treated fabrics is unexpected since silicones are considered to provide water repellency properties to fabrics rather than enhanced rewettability. Thus, the opposite result would be expected. Accordingly, the present invention provides compositions and methods of fabric treatment possessing significant advantages over prior art materials and processes as exemplified by Dumbrell et al.